Lubricants having improved anti-wear and anti-corrosion properties

ABSTRACT

A LUBRICANT, ESPECIALLY FOR SUPERSONIC JET AIRCRAFT ENGINES, IS BASED ON A HINDERED ESTER AND CONTAINS A DIALKYL HYDROGEN PHOSPHATE AS A LOAD-CARRYING ADDITIVE, A COPPER PASSIVATOR AND AN AROMATIC AMINE ANTIOXIDANT. THE LUBRICANT MAY ALSO CONTAIN A LEAD CORROSION INHIBITOR AND A NEUTRAL PHOSPHATE.

3,697,427 Patented Oct. 10, 1972 s 697 421 LUBRICANTS nAvu io IivIPRovEn ANTI-WEAR AND ANTI-CORROSION PROPERTIES Derek Clark Byford, Staines, and Howard Bernard Silver,

Hinchley Wood, England, assignors to The British Petroleum Company Limited, London, England No Drawing. Continuation of abandoned application Ser. No. 653,681, July 17, 1967. This application Apr. 30, 1971, Ser. No. 139,182

Int. Cl. C10m 1/34, 1/46 US. Cl. 252-493 7 Claims ABSTRACT OF THE DISCLOSURE A lubricant, especially for supersonic jet aircraft engines, is based on a hindered ester and contains a dialkyl hydrogen phosphate as a load-carrying additive, a copper passivator and an aromatic amine antioxidant. The lubricant may also contain a lead corrosion inhibitor and a neutral phosphate.

This application is a continuation of Ser. No. 653,681, filed July 17, 1967, now abandoned.

This invention relates to synthetic lubricating compositions that have had their anti-wear and anti-corrosion properties improved by the addition of small amounts of certain additives.

The use of certain acid phosphorus compounds as loadcarrying or anti-Wear additives for synthetic lubricating oils has previously been suggested but their use has been associated with a number of drawbacks. For example they tend, in general, to be corrosive if used at the concentrations previously preferred and at the very high temperatures that modern aviation turbine lubricants have to withstand and we have found that some of them are not compatible with metal passivators that are added to improve the lubricant with respect to its corrosivity towards metals, particularly copper.

We have now found that by using a combination of certain amounts of certain di-alkyl hydrogen phosphates with metal passivators it is possible to produce synthetic lubricant formulations having very good anti-wear and anti-corrosion properties at very high temperatures. By the addition of suitable antioxidants to these formulations it is possible in some cases to produce products having the properties required to lubricate the engines of modern supersonic jet aircraft.

According to the invention, there is provided a lubricating composition comprising an ester basestock consisting of one or more liquid neutral polyesters that have been prepared by reacting together under esterification conditions and in one or more stages:

(i) a monoand/or polyhydric alcohol having -15, preferably 5-10, carbon atoms per molecule and having no hydrogen atoms attached to any carbon atom in a 2 position with respect to any OH group, and

(ii) a monoand/or polycarboxylic acid having 214,

preferably 3-12, carbon atoms per molecule,

the base oil having dissolved therein:

(a) 0.005 to 0.15% wt., preferably less than 0.08% wt.,

of a dihydrocarbon hydrogen phosphate of the formula (RO) P(O)OH where the groups R (which are not necessarily the same in any given molecule) are alkyl, cycloalkyl, aryl, alkaryl or aralkyl groups having up to 20 carbon atoms, preferably alkyl or cycloalkyl groups having up to 10 carbon atoms, e.g. butyl, 2-ethy1bexyl or cyclohexyl,

(b) 0.005 to 1.5, preferably 0.01 to 0.5, percent wt. of a copper passivator, and

(c) 0.5 to 6.0, preferably 2.5 to 5, percent wt. of an aromatic amine antioxidant.

The additive concentrations quoted in this specification are based on the ester basestock. It is to be understood that the composition may contain more than one member of each of the classes of ingredients specified.

Copper passivators are a Well-known class of materials, the function of which is to reduce the extent to which copper is attacked by corrosive substances. The copper passivator used in the compositions according to the invention must, of course, be soluble in the basestock. The efiect of this additive is to reduce the corrosion on engine component materials when exposed to the lubricant for long periods at high temperatures and in the presence of air. The effectiveness of metal passivators can be measured by corrosion tests in which the protection of structural metals can be observed. Copper is the most critical metal involved in such tests and it has been found that if this metal can be effectively passivated, then the corrosion of the other metals present is negligible small, except for lead. Suitable classes of copper passivator include:

1) Those of the azole type such as imidazole, pyrazole, triazole and their derivatives, e.g. benzotriazole, methylbenzotriazole, ethylbenzotriazole, butylbenzotriazole, dodecylbenzotriazole, methylene bis benzotriazole and naphthotriazole.

(2) Salicylaldehyde semicarbazone and its C to C alkyl derivatives, e.g. methyl and isopropyl salicylaldehyde semicarbazone.

(3) Condensation products of salicylaldehyde and hydrazine derivatives, and fatty acid salts of such condensation products. A particularly suitable hydrazine derivative is aminoguanidine and suitable fatty acids are those having 2 to 24 carbon atoms.

Particularly effective copper passivators are methylene bisbenzotn'azole and salts of l-salicylalaminoguanidine and fatty acids having 13 to 18 carbon atoms, e.g. palmitic acid. Where the lubricant is intended for use in engines containing lead alloy components, it is desirable to include a lead corrosion inhibitor in the blend, usually at a concentration of 0.01 to 1.0, preferably 0.05 to 0.25, percent Wt. Suitable lead corrosion inhibitors are C, to C alkyl gallates (e.g. propyl gallato), neopentyl glycol disebacate, sebacic acid and quinizarin. Propyl gallate is preferred; it does not affect the other properties of the lubricant.

Suitable aromatic amine antioxidants include phenothiazine, iminodibenzyl, diphenylamine, phenyl-alphanaphthylarnine and phenyl-betamaphthylamine. Particularly suitable are the alkylated (e.g. the C to C alkylated) aromatic amines, especially those of the formula R C H NHC H R Where the R groups are alkyl groups having up to 14 carbon atoms (not necessarily the same at each occurrence in any given molecule), preferably octyl or nonyl groups, p,p-dioctyldiphenylamine is particularly efiFective. Other particularly suitable alkylated aromatic amines include the monoand di-C;

to C alkyl (e.g. the dioctyl and dinonyl) phenothiazines, iminodibenzyls, diphenyl-p-phenylenediamines and phenylnaphthylamines. In some cases it may be desirable to use a mixture of antioxidants e.g. a mixture of an alkylated diphenylamine (e.g. dioctyldiphenylamine) and an alkylated phenyl naphthylamine (e.g. a mono-octylphenyl naphthyla'mine) H The expression ,polyester is used in this specification to mean an ester having at least two ester linkages per molecule. The expression neutral is used to mean a fully esterified product. It is to be understood that in the esterification reaction referred to above there may be used more than one of any of the reactants mentioned, e.g. a mixture of monocarboxylic acids, and, in any case, the neutral ester product of the esterification reaction will sometimes consist of a mixture of different ester molecules, so the expression polyester is to be construed in this light.

Polyesters that are especially suitable as high temperature base oils in the compositions according to the invention are those made from the following acids and al- 1 cohols: caprylic acid, capric acid, caproic acid, enanthic acid, pelargonic acid, valeric acid, pivalic acid, propionic acid, butyric acid, 2-ethylhexanoic acid, adipic acid, sebacic acid, azelaic acid, 2:2:4-trimethylpentanol, neopentyl alcohol, neopentyl glycol, trimethylolethane, trimethylolpropane, pentaerythritol and dipentaerythritol.

Examples of such especially suitable polyesters are:

(a) esters" of E trimethylolpropane, trimethylolethane, pentaerythritoland/or di-pentaerythritol with one or more monocarboxylic acids having 3-10 carbon atoms, paflticularly those mentioned in the previous paragraph, an

(b) complex esters prepared from trimethylolpropane,

sebacicand/or azelaic acid, and one or more monocarboxylic acids having 3-10 carbon atoms, particularly those mentioned in the previous paragraph. Most suitably the trimethylolpropane and dicarboxylic acid are reacted in the molar ratio of 1:0.050.75, preferably 120075-04, the amount of monocarboxylic acid being sufiicient to provide a carboxyl/hydroxyl balance in the reactants.

The good anti-wear or load-carrying properties of the composition according to the invention may be still further improved by the addition of a neutral phosphate of the formula (R O) PO where the R groups are alkyl, cyclo alkyl, aryl, alkaryl or aralkyl groups (not necessarily the same in any given molecule) and the total number of carbon atoms in the molecule is 3-60, preferably 3-30. The amount of such neutral phosphorus compound should be 0.01 to 10%, preferably 0.5 to 5%, by weight of the composition. Preferred neutral phosphates are those in which the R groups are alkyl or cycloalkyl groups having up to 10 carbon atoms, phenyl groups, tolyl groups or xylyl groups.

EXAMPLES A number of compositions according to the invention and also a number of comparative compositions were tested for anti-wear or load carrying properties using the well-known IAE gear machine and for anti-corrosion properties and oxidation stability in a high temperature oxidation/ corrosion test. The tests were of the type specified in government and engine manufacturers specifications for lubricants for use in aero turbine engines for modern jet aircraft.

In the gear test, a set of gears was sprayed with the lubricant to be tested at 200 C. and the gears were run at 2000 rpm. while a load was applied by means of a weighed lever arm. The load on the lever arm when scufling of the gears occurredwas noted.

In the high temperature oxidation/corrosion test, the oil was held at 425 F. (218 C.) for 48 hours in the presence of five metals and with air bubbling through the oil at 5 litres/hour. The metal weight change and the increase in the viscosity and acid value of the oil was measured. The cleanliness of the oil is also assessed in this test by measuring the amount of insoluble material formed.

The following base oils were used in the lubricating compositions tested:

AA complex ester prepared by reacting together under esterification conditions caprylic acid, 1:1: l-trimethylolpropane and sebacic acid in the molar ratio of 28:10:1- and using a catalyst.

B-A blend of four parts by weight of a neutral ester of pentaerythritol and a mixture of C -C monocarboxylic straight-chain acids with one part by weight of a. neutral ester of dipentaerythritol and the same mixture of carboxylic acids.

The additives used in the compositions were as follows:

DBHR=Dibutyl hydrogen phosphate: (C H O) P(O) OH.

SAGP=Salt of l-salicylalaminoguanidine and a mixture of fatty acids having 13-18 carbon atoms.

MBBTZ=Methylene bis-benzotriazole.

Antioxidant: In all cases this was a blend of 3 parts of p,p'-dioctyldiphenylamine and 1 part of mono-octyl phenyl beta naphthylamine. This has been found to be the best combination from the point of view of cleanliness and both extended and accelerated oxidation tests.

'I'I'PI=Tritoly1 phosphate.

PG=Propyl gallate.

The lubricating compositions used in the tests are shown in Tables 1 and 2. The figures represent parts by weight.

TABLE 1.COMPOSITION OF BLENDS ACCORDING TO THE INVENTION Composition Base oilA 100 100 100 100 Base 0113 100 100: DBHP 0.02 0.02 0.02 0.02 0.02 0.02 0.02 SAGP- 0.1 0.1 0.1 0.1 0.1 MBB 0.02 0.02 Antioxidant 4.0 4.0 4.0 i 4.0 4.0 4.0 4.0 TTP 2.0 2.0 2.0 2.0 PG 0.1 0.1 0.1 0.1 0.1

TABLE 2.-COMPOSITION OF COMPARATIVE BLENDS Composition Base oilA 100 The results of the tests are given in Tables 3, 4 and 5.

TABLE 3.LOAD CARRYING TEST The superior load-carrying properties of the compositions according to the invention containing minute proportions of dibutyl hydrogen phosphate as compared with the other compositions is clearly shown.

(b) 0.005 to 1.5% wt. of a copper passivator,

(c) 0.5 to 6.0% wt. of an aromatic amine antioxidant,

and

(d) 0.01 to 1% wt. of C to C alkyl gallate.

TABLE 4.OXIDATION/CORROSION TEST Viscosity Acidity increase increase, Metal weight change, mg.lcm. at 100 F., mg.

percent KOH/g. Mg Al Cu Ag Fe Desirable limits Not more Not more +0.3 0. +0.3 +0.3 +0.3 Insoluthen 50 than 5 to 0.3 to 0.3 to .3 to 0.3 to 0.3 bles, mg.

Composition:

22 45 1. 7 0. 03 0. 01 1. l4 0. 13 0. 03 53 3. 0. 02 Nil 0. 75 0. 05 0. 1 0 44 3. 6 0. O3 0. 01 -1. l4 0. l3 0. 03 0 85 1. 3 0. 04 -0. 03 0. 07 --0. 12 0. 04 0 40 2. 5 Nil 0. 01 0. O9 0. 06 +0. 01 0 38 2. 2 Nil +0. 02 +0. 02 0. 05 +0. 06 0 36 3. 0 Nil +0. 3 Nil -0. 03 +0. 04 0 64 1. 7 Nil 0. 06 1. 81 0. 11 0. 03 0 56 1. 8 0. 05 0. 01 0. 89 0. 10 Nil 0 36. 5 0. 5 Nil 0. 04 0. 12 0. 12 0. 01 0 45 1. 7 0. 03 0. 02 0. 15 0. 13 +0. 03 0 The results quoted in Table 4 show the exceptionally high resistance to oxidation and corrosion and the outstanding cleanliness of the lubricating compositions according to the invention.

Compositions 2-7 gave much better results in these tests than compositions 22, 23, 25, 27 and 29 which did not contain a copper passivator.

Table 5 below shows that the substantial improvement in load carrying given by the addition of minute quantities of dibutyl hydrogen phosphate is achieved without significantly damaging the oxidation/corrosion properties of the compositions.

2. A lubricating composition according to claim 1, in which the polyester is an ester of trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol or mixtures thereof with at least one monocarboxylic acid hav ing 3 to 10 carbon atoms.

3. A lubricating composition according to claim 1, in which the polyester is a complex ester prepared from trimethylolpropane, sebacic acid, azelaic acid, and mixtures of said acids and at least one monocarboxylic acid having 3 to 10 carbon atoms.

4. A lubricating composition according to claim 1, in which the copper passivator is selected from the group TABLE 6 Viscosity Acidity increase increase, Metal weight change, mgz/cm. Insol- Scufiing at 100 F., mg. ubles, load, lb. percent KOH/g. Mg Al Cu Ag Fe mg.

Composition:

36 41.7 4.8 0.06 0.06 -0.12 0.09 Nil 0 80 40 2.5 Nil 0.01 0.09 0.06 +0.01 0

36.5 0.5 Nil 0.04 0.12 0.12 0.01 0 41 38 1.25 +0.01 Nil 0.11 0.03 Nil 0 What we claim is:

1. A lubricating composition comprising an ester basestock consisting of at least one liquid neutral polyester that has been prepared by reacting together under esterification conditions and in at least one stage:

(i) an aliphatic alcohol selected from the group consisting of monohydric alcohols, polyhydric alcohols, and mixtures thereof, said alcohol having 5-10 carbon atoms per molecule and having no hydrogen atoms attached to any carbon atom in a 2 position with respect to any --OH group, and

(ii) an aliphatic acid selected from the group consisting of monocarboxylic acid, polycarboxylic acid and mixtures thereof, said acid having 3-12 carbon atoms per molecule,

the base oil having dissolved therein:

(a) 0.005 to 0.08% of a dial-kyl hydrogen phosphate of the formula (RO) *P(O)OH where R is selected from the group consisting of an alkyl or cycloalkyl group having up to 10 carbon atoms,

consisting of methylene bis benzotriazole, benzotriazole, methyl benzotriazole, ethyl benzotriazole, butyl benzotriazole, dodecylbenzotriazole, naphthotriazole and salts of l-salicylalaminoguanidine and at least one fatty acid having 13 to 18 carbon atoms.

5. A lubricating composition according to claim 1, in which the antioxidant is selected from the group consisting of an alkylated aromatic amine of the formula R C H NHC H4R where the groups R are alkyl groups having up to 14 carbon atoms, and a mixture of said compound R C H N'I-IC H R with a mono-C to C alkyl phenyl naphthylamine or (ii-C to C alkyl phenyl naphthylamine.

6. A lubricating composition according to claim 1, which also contains 0.5 to 5% wt. of a neutral phosphate of the formula (R O) PO where the groups R are selected from the group consisting of alkyl groups having up to 10 carbon atoms, cycloalkyl groups having up to 10 carbon atoms, phenyl groups, tolyl groups and xylyl groups.

3,697,427 7 8 7. A lubricating composition according to claim 1, OTHER REFERENCES in which the dialkyl hydrogen phosphate is dibutyl hy- Klaus et ah: Chemical so; ,PreprintS Petro drogen phosphate. i

References Cited leum Sect1on, vol. 5, No. 2-B (1960), pp. B197-B214. UNITED STATES PATENTS 5 DANIELE. WYMAN, Primary Examiner 2,235,853 6/1942 w i g et al. 25234.7 X W. H. CANNON, Assistant Examiner 3,247,111 4/1966 'Oberright et a1 252--34.7

US. Cl. X.R.

FOREIGN PATENTS 10 252-34, 49.8, 50, 56 S 986,062 3/1965 Great Britain. 

